objective-c MKMapView center on user location

Question

I'm trying to zoom into the user location as the center reference for the screen. I have this code:

MainViewController.h

#import <UIKit/UIKit.h>
#import "FlipsideViewController.h"
#import <MapKit/MapKit.h>
#import <CoreLocation/CoreLocation.h>

IBOutlet MKMapView *mapView;

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate, MKMapViewDelegate> {
   MKMapView *mapView;
}
@property (nonatomic, retain) IBOutlet MKMapView *mapView;

MainViewController.m

@implementation MainViewController
@synthesize mapView;

 - (void)viewDidLoad {
    [super viewDidLoad];
    mapView = [[MKMapView alloc]
           initWithFrame:self.view.bounds
           ];
    mapView.showsUserLocation = YES;
    mapView.mapType = MKMapTypeHybrid;
    mapView.delegate = self;
    [self.view addSubview:mapView];
}

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation {
    MKCoordinateRegion region;
    MKCoordinateSpan span;
    span.latitudeDelta = 0.005;
    span.longitudeDelta = 0.005;
    CLLocationCoordinate2D location;
    location.latitude = userLocation.coordinate.latitude;
    location.longitude = userLocation.coordinate.longitude;
    region.span = span;
    region.center = location;
    [mapView setRegion:region animated:YES];
 }

Now I'm only getting a build warning on the last line [mapView setRegion:region animated:YES] stating: 'local declaration of 'mapView' hides instance variable'

Deepak Danduprolu · Accepted Answer · 2011-05-29T21:39:44.350

72

When you do mapView.showsUserLocation = YES;, you ask it to retrieve the user location. This doesn't happen instantly. As it takes time, the map view notifies its delegate that a user location is available via the delegate method mapView:didUpdateUserLocation. So you should adopt the MKMapViewDelegate protocol and implement that method. You should move all your zooming-in code to this method.

Setting the delegate

- (void)viewDidLoad {
    [super viewDidLoad];
    mapView = [[MKMapView alloc]
           initWithFrame:CGRectMake(0, 
                                    0,
                                    self.view.bounds.size.width, 
                                    self.view.bounds.size.height)
           ];
    mapView.showsUserLocation = YES;
    mapView.mapType = MKMapTypeHybrid;
    mapView.delegate = self;
    [self.view addSubview:mapView];
}

Updated delegate method

- (void)mapView:(MKMapView *)aMapView didUpdateUserLocation:(MKUserLocation *)aUserLocation {
    MKCoordinateRegion region;
    MKCoordinateSpan span;
    span.latitudeDelta = 0.005;
    span.longitudeDelta = 0.005;
    CLLocationCoordinate2D location;
    location.latitude = aUserLocation.coordinate.latitude;
    location.longitude = aUserLocation.coordinate.longitude;
    region.span = span;
    region.center = location;
    [aMapView setRegion:region animated:YES];
}

edited May 29 '11 at 21:39

answered May 29 '11 at 19:48

Deepak Danduprolu

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1

I am extremely new to objective-c so bear with me...how I do call the didUpdateUserLocation method from within the didViewLoad method? – sadmicrowave May 29 '11 at 20:02
You don't. You adopt the protocol as @Srikar pointed out and as you seem to have done and then assign yourself as its delegate like `mapView.delegate = self;`. The map view will notify you on its own when it has the necessary information. – Deepak Danduprolu May 29 '11 at 20:09
@Deepak @Srikar - please view my original post to see what is happening now after I updated things.... – sadmicrowave May 29 '11 at 20:21
@sadmicrowave Have you set the delegate? – Deepak Danduprolu May 29 '11 at 20:24
@Deepak - you should how to set the delegate but where do I do that? I tried putting it in the viewDidLoad and in the DidUpdateUserLocation methods and I got a build error "MainViewController does not implement the MKMapViewDelegate protocol". – sadmicrowave May 29 '11 at 20:26
@Deepak - also, thats all I have in the console to show you - there is nothing else – sadmicrowave May 29 '11 at 20:27
@Deepak - like I said (check my OP for an update of the delete part also) I get an error "MainViewController does not implement the MKMapViewDelegate protocol" on this line. – sadmicrowave May 29 '11 at 20:44
2

Have you done this `@interface MainViewController : UIViewController ` like Srikar said? – Deepak Danduprolu May 29 '11 at 20:49
2

And one final thing the delegate method is `- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation` and not the method shorthand `mapView:didUpdateUserLocation:` – Deepak Danduprolu May 29 '11 at 20:53
@Deepak - my bad - I didn't put MKMapViewDelegate inside the @interface declaration - after doing this the zoom executes successfully. One last problem though is after implementing your last two suggestions I am now getting build warnings for location.longitute, location.latitude, and [mapView setRegion...] stating: 'location declaration of mapView hides instance variable' Do you know what this could be from? – sadmicrowave May 29 '11 at 21:10
yeah you have a property called `userLocation` and one of the arguments of the delegate method is also `userLocation`. Change the latter to `aUserLocation`. It should work. – Deepak Danduprolu May 29 '11 at 21:15
I took the mapView off the front of mapView.userLocation.coordinate.latitude, etc. changing it to userLocation.coordinate.latitude and it fixed those two lines but I'm still receiving the error for [mapView setRegion:region animated:YES]. – sadmicrowave May 29 '11 at 21:26
Which error are you getting? And can you update the question with your latest code? – Deepak Danduprolu May 29 '11 at 21:28
2

Local variables are masking the instance variables. Adjusted the delegate method and edited it into my answer. – Deepak Danduprolu May 29 '11 at 21:40

score 3 · Answer 2 · answered May 29 '11 at 19:39

3

In your interface you forgot to inherit MapViewDelegate -

#import <MapKit/MapKit.h>

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate, MKMapViewDelegate> 
{
   MKMapView *mapView;
}
@property (nonatomic, retain) IBOutlet MKMapView *mapView;

Rest seems fine.

answered May 29 '11 at 19:39

Srikar Appalaraju

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I added your @property line and still am receiving the same problem error – sadmicrowave May 29 '11 at 20:02
I changed some stuff in my OP please check it again – sadmicrowave May 29 '11 at 20:22

objective-c MKMapView center on user location

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